Non-glycosylated, recombinant human IL 2 in reduced form

ABSTRACT

A biologically active, non-glycosylated recombinant human Interleukin 2 (R-hIL 2 ) in reduced form, process for its preparation and method of use.

PRIOR APPLICATIONS

This application is a continuation of U.S. Pat. application Ser. No. 204,650 filed Mar. 1, 1994 which is a continuation of U.S. Pat. application Ser. No. 869,803 filed Apr. 16, 1992 which is a continuation of U.S. Pat. application Ser. No. 384, 986 filed Jul. 24, 1989, all now abandoned.

Natural human IL₂ which is a lymphokine stimulating the proliferation of activated T cells, has 3 cysteines localized at position 58, 105 and 125 in the amino acid sequence of the protein. The cysteines at position 58 and 105 are joined by a disulfide bridge whereas the cysteine at position 125 has a free sulfhydryl group (Robb et al., Proc. Natl. Acad. Sci. (1984), Vol. 81 page 6486-6490).

The processes for the preparation of human IL₂ alleles or derivatives, by the technology of recombinant DNA are described. For example, Taniguchi et al., Nature (1983) 302 305-310 and Devos et al., Nucleic Acids Research (1983) Vol. 11) page 4307-4323 have described the cloning of the human IL₂ gene and its expression in micro-organisms, and Ju et al., J. Biol. Chem (1987) Vol. 262 p. 5723-5731 have obtained the expression of recombinant derivatives of IL₂.

It is known that when IL₂ is accumulated in a micro-organism in a state of insoluble granules, it is found in reduced form containing 3 thiol groups and is void of activity (Japanese Patent Application J6 1,257,931). It was therefore admitted that to have available an active IL₂ there had to be an oxidation process of the reduced protein accumulated in the granules. To do this, after dissolving the protein in a denaturizing medium, the formation of a suitable disulfide bridge 58-105 which needs renaturization, was carried out in a controlled oxidizing medium. Different methods have been described such as oxidation by oxygen alone (auto-oxidation in air) or in the presence of cupric ions, or of a weak oxidant such as a thiol or by a thiol-disulfide mixture. (Tsuji, T et al., Biochemistry (1987) Vol. 26 p. 3129-3134).

After oxidative renaturization, purification by chromatography is necessary to eliminate the oxidation products corresponding to the formation of isomeric intramolecular bridges 58-125 and 105-125 as well as the intramolecular bridges which have been shown to be inactive and can be separated by inverse phase chromatography according to Wang et al., Science (1984) Vol. 224, p 1431-1433 or Browing et al., Anal. Biochem. (1986) Vol. 155, p 123-128).

Obtaining homogeneous oxidized recombinant IL₂ having suitable biological activity, starting from the accumulated protein in the form of granules, therefore raises certain technical problems, whatever the process used because several purification steps are needed which leads to a lower yield of the desired product.

Two other references which relate to IL₂ can be cited: European Patent EP 0145390 and U.S. Pat. No. 4,738,927.

OBJECTS OF THE INVENTION

It is an object of the invention to provide novel non-glycosylated, recombinant human Interleukine 2 in reduced form and a process for its preparation without reoxidation.

It is another object of the invention to provide novel immunomodulating compositions and method.

These and other objects and advantages of the invention will become obvious from the following detailed description.

THE INVENTION

One aspect of the invention relates to non-glycosylated, recombinant human Interleukine 2 having the following sequence of amino acids:

    ______________________________________                                         X-Ala Pro Thr Ser Ser Ser Thr Lys Lys Thr Gln Leu Gln Leu Glu                  His Leu Leu Leu Asp Leu Gln Met Ile Leu Asn Gly Ile Asn Asn Tyr                Lys Asn Pro Lys Leu Thr Arg Met Leu Thr Phe Lys Phe Tyr Met Pro                Lys Lys Ala Thr Glu Leu Lys His Leu Gln Cys Leu Glu Glu Glu Leu                Lys Pro Leu Glu Glu Val Leu Asn Leu Ala Gln Ser Lys Asn Phe His                Leu Arg Pro Arg Asp Leu Ile Ser Asn Ile Asn Val Ile Val Leu Glu                Leu Lys Gly Ser Glu Thr Thr Phe Met Cys Glu Tyr Ala Asp Glu Thr                Ala Thr Ile Val Glu Phe Leu Asn Arg Trp Ile Thr Phe Cys Gln Ser                Ile Ile Ser Thr Leu Thr                                                        ______________________________________                                    

as well as the allels or derivatives of this sequence in which X is methionine or hydrogen and the three cysteines at position 58, 105 and 125 are in reduced form, and having a biological activity comparable to that of oxidized IL₂ having the same sequence and containing a disulfide bridge at position 58-105.

By allels and derivatives, the sequences of one or more amino acids other than cysteines 58, 105 and 125, modified by substitution, deletion or addition are included, to the extent that these products keep the biological activity characteristic of reduced IL₂. Obtaining such modifications is well known in the method of recombinant DNA, for example by the guided mutagenesis techniques reviewed by Lather et al in Genetic Engineering Academic Press (1983) 31-50 or Smith et al., Genetic Engineering Principals and Methods, Plenum Press (1981) 3 1-32.

By reduced form, it is understood that the cysteine residues, which IL₂ contains, have a free sulfhydryl group, the determination of which is, for example, carried out by spectrophotometry with dithiodipyridine as the thiol reagent. The biological activity of the reduced form dealt with in the invention is determined, similar to that of the corresponding oxidized form containing the disulfide bridge 58-105, by measure ment of the proliferation of the leukemic cellular lines of mice depending on IL₂ CTll-2, with a colorimetric test with tetrazolium salt (Mossmann, TJ. Immunol Meth. (1983) Vol. 65, p 55-63).

The invention also relates to a non-glycosylated, recombinant human IL₂ having the following sequence of amino acids:

    ______________________________________                                         XAla ProThrSerSerSerThrLysLysThrGlnLeuGlnLeuGlu                                HisLeuLeuLeuAspLeuGlnMetIleLeuAsnGlyIleAsnAsnTyr                               LysAsnProLysLeuThrArgMetLeuThrPheLysPheTyrMetPro                               LysLysAlaThrGluLeuLysHisLeuGlnCysLeuGluGluGluLeu                               LysProLeuGluGluValLeuAsnLeuAlaGlnSerLysAsnPheHis                               LeuArgProArgAspLeuIleSerAsnIleAsnValIleValLeuGlu                               LeuLysGlySerGluThrThrPheMetCysGluTyrAlaAspGluThr                               AlaThrIleValGluPheLeuAsnArgTrpIleThrPheCysGlnSer                               IleIleSerThrLeuThr                                                             ______________________________________                                    

as well as the allels or derivatives of this sequence in which X is methionine or hydrogen and the three cysteines at position 58, 105 and 125 are in reduced form, and having a biological activity of at least 0.5×10⁷ U/mg. The unit of IL₂ activity is defined as the quantity which produces 50% of the maximum response in the test. A sample "Biological Response Modifier Program (BRMP) reference human reagent IL₂ (Jurkat)" provided by the the National Cancer Institute (NCI) is used as a standard.

More precisely, the invention relates to non-glycoslated, recombinant human interleukine 2 having the following sequence of amino acids:

    ______________________________________                                         X-Ala Pro Thr Ser Ser Ser Thr Lys Lys Thr Gln Leu Gln Leu Glu                  His Leu Leu Leu Asp Leu Gln Met Ile Leu Asn Gly Ile Asn Asn Tyr                Lys Asn Pro Lys Leu Thr Arg Met Leu Thr Phe Lys Phe Tyr Met Pro                Lys Lys Ala Thr Glu Leu Lys His Leu Gln Cys Leu Glu Glu Glu Leu                Lys Pro Leu Glu Glu Val Leu Asn Leu Ala Gln Ser Lys Asn Phe His                Leu Arg Pro Arg Asp Leu Ile Ser Asn Ile Asn Val Ile Val Leu Glu                Leu Lys Gly Ser Glu Thr Thr Phe Met Cys Glu Tyr Ala Asp Glu Thr                Ala Thr Ile Val Glu Phe Leu Asn Arg Trp Ile Thr Phe Cys Gln Ser                Ile Ile Ser Thr Leu Thr                                                        ______________________________________                                    

in which X is methionine or hydrogen and the three cysteines at position 58, 105 and 125 are in reduced form and having biological activity similar to that of natural human IL₂.

By similar activity it is understood the same specific activity as that of natural IL₂ isolated from the leukemic Jurkat cells, that is to say 1.3×10⁷ U/mg (reference BRMP), or an activity differing at the most by 25% of this specific activity. The sequence of reduced IL₂ dealt with in the invention optionally has a supplementary N-terminal methionine according to the transformed micro-organism, such as E. coli, in which it is expressed. In a preferred embodiment of the invention, the sequence containing methionine is preferred, but a mixture of a product containing methionine with a product which does not contain methionine or the product which is deprived of methionine can also be used.

Another aspect of the invention relates to a process for the preparation of reduced, non-glycosylated, recombinant human IL₂ comprising extracting IL₂ accumulated in the form of granules in a transformed micro-organism,--by solubilization in a reducing medium with a chaotropic agent, purification by precipitation followed by inverse phase, high performance liquid chromatography with an acid eluant, and characterized in that:

a) if necessary, the principal fraction eluted in the said chromatography is submitted to a cooling stage at a temperature in the range of -20° C., then to separation of the aqueous phase which

b) is diluted in an acid medium, then is chromatographed on another inverse phase, high performance liquid chromatography column in an acid medium to obtain the said IL₂.

The recombinant IL₂ produced in the form of granules, because of the high rate of expression, by a transformed micro-organism such as E. coli, can be solubilized by known methods with a concentrated solution of a chaotropic agent such as 6 to 8M solution of guanidine salt, then purified by inverse phase, high performance liquid chromatography (hereafter called RP-HPLC) with commercially avaiable supports, preferably of grafted silicas such as C3, C4, C8 or C18, with an acid eluant having a pH value between 1 and 4. The IL₂ can be eluted from the column by a gradient system comprising an organic acid such as acetic acid or trifluoroacetic acid (hereafter called TFA) and an organic solvent such as acetonitrile. The principal fraction, the elution of which is detected by spectrophotometry at 280 nm, is the raw material for the optional cooling stage which forms part of the process of the present invention.

By cooling, it is understood that the said principal fraction collected at ambient temperature is placed in an environment with a temperature on the order of -20° C., which allows the progressive formation of a solid aqueous phase, the supernatant fraction of which can be eliminated by decanting. The aqueous phase, optionally separated in such a way, serves, after dilution, as the raw material for the RP-HPLC in the acid medium described below which forms a part of the process of the invention.

The dilution of the aqueous phase is carried out in an acid medium having a pH value of from 1 to 4, and preferably from 2 to 3. The diluted aqueous phase is chromatographed on an inverse phase column, using commercially available supports such as grafted silicas C3, C4, C8 or C18 having pores of a suitable size for use with proteins, for example of a diameter of at least 150 A°. The elution of IL₂ includes the use of a gradient of increasing concentration of a lower alcohol miscible with water and containing an organic acid.

The process of the invention is notably characterized in that the optional cooling stage is carried out in an aqueous solution of acetonitrile containing approximately 0.1% trifluoroacetic acid, in that the dilution is carried out with an aqueous solution of an organic acid such as citric acid and in that the said IL₂ is eluted in the second chromatograph with a solution containing isopropanol, water and an organic acid such as citric acid. The aqueous solution of acetonitrile containing approximately 0.1% of TFA, which is the preferred mixture submitted to the optional cooling stage of the invention, corresponds to the principal fraction eluted in the first chromatography. More preferably, the dilution of the aqueous phase is carried out immediately, either after the optional separation, or after the first chromatography. This dilution is carried out by addition, preferably, of at least 2 volumes of water containing 0.5 to 2% of an organic acid such as formic acid, acetic acid, propionic acid, trifluoroacetic acid or citric acid, more preferably by the addition of approximately 2 volumes of water containing 0.5% of citric acid.

The second chromatograph which forms a part of the process of the invention consists of submitting the aqueous phase, which is optionally separated after the cooling stage and then diluted, to a RP-HPLC using commercially available supports such as grafted silicas C3, C4, C8 or C18 having pore diameters of at least 150° A. The preferred support is a grafted silica C4 VYDAC 300° A which is a silica gel which has butyl groups grafted in covalent manner, of which the pores have a diameter of 300° A and the particles have an average size of 15 to 20 microns.

The elution of IL₂ dealt with in the process of the invention is carried out with a gradient system comprising an alcohol such as propanol or isopropanol and an organic acid such as formic acid, acetic acid, propionic acid, trifluoroacetic acid or citric acid. The preferred mixture comprises isopropanol, water and citric acid preferably at 0.5 to 2%, more preferably at 0.5% and allows, with a gradient system of increasing concentrations of isopropanol, the elution of a lower fraction at approximately 48% of isopropanol, then a higher fraction at approximately 59% of isopropanol, this latter comprising non-glycosylated, active recombinant human IL₂ in reduced form.

The subject of the invention is also non-glycosylated, recombinant human IL₂ in reduced form which can be obtained by the process described above. The said fraction obtained can be kept at approximately 0° to -20° C. as it is stable under these conditions. The isopropanol can also be eliminated by azeotropic distillation in a vacuum. The solution obtained can be kept at +4° C. or the IL₂ of the present invention can be isolated immediately by lyophilization.

The invention also relates to a variation of the process in which the principal fraction is not submitted to the cooling stage and separation of the aqueous phase. The diluted principal fraction obtained by this claimed variation of the process can also be kept at +4° C. as it is stable and constitutes the raw material for the second chromatography which forms part of the process of the invention.

When the thiol groups are measured, the IL₂ obtained by the invention has 3 free sulfhydryl groups and shows a specific activity of 0.7 to 1.3×10⁷ U/mg in the proliferation test of the CTLL-2 lines which is similar to that of natural IL₂. This activity justifies the use of the non-glycosylated, recombinant human IL₂ in reduced form for use as a medicament in the same manner as natural IL₂, in a variety of ways to use its immuno-modulating activity as well as its antitumoral activity which have been described for example by Fletcher et al., Lymp-hokine Research Vol. 6 (1987) p 47-57 and which comprises, for example, the proliferation of T lymphocytes, the induction of the cytotoxicity of the NK (natural killer) cells and the LAK (lymphokine activated killer) cells, the restoration of cellular immunity, a protective effect against infection in cases of immunity deficiencies or an adjuvant effect with regard to vaccines. The administration can be carried out directly or can be an administration associated with a method of adoptive immuno-therapy which was described by Rosenberg et al., in N. Engl.J. Med. (1985) Vol. 313, p 1485-1492.

As with natural IL₂, the IL₂ of the invention can be used by itself or with other immuno-modulator agents such as alpha interferon, gamma interferon and/or other therapeutic agents.

The immunomodulating compositions of the invention are comprised of an immunomodulating effective amount of the non-glycosylated recombinant human IL₂ in reduced form and an inert pharmaceutical carrier.

The compositions may be formed, for example by removing isopropanol from the above aqueous solutions of the product described above by azetropic distillation under reduced pressure and after the addition of a water-soluble loading agent, the product is lyophilized.

The water-soluble loading agent is a substance which will not change the initial pH when the product is reconstituted and examples are sugars such as glucose, ribose, saccharose, maltose and trehalose and reduced sugars such as mannitol.

Mannitol is preferred and is added at a concentration of from 10 to 50 mg/ml, preferably about 50 mg/ml when the concentration of IL₂ of the present invention is between 0.05 amd 1 mg/ml, depending on the dose to be administered. The solution is filtered under sterile conditions in the absence of oxygen and divided into dosing flasks and lyophilized. The lyophilized mixture can be reconstituted by injection in the flask of distilled water suitable for parenteral injection.

When the composition is to be used for perfusion administration, it is more particularly characterized in that it contains besides non-glycosylated, recombinant human IL₂ in reduced form, water and an organic acid such as citric acid. Such a composition can be obtained starting from the lyophilized pharmaceutical composition of the invention which is dissolved in the presence of an appropriate vehicle which contributes to the stability of the active principle during the time of the perfusion, for example glucose. The preferred conditions consist in diluting the lyophilized mixture reconstituted by injection of distilled water, by introducing it in a perfusion pocket containing a volume of glucose at a concentration of 50 mg/ml determined as suitable for the dose to be administered.

The novel method of the invention for inducing immuno-modulating activity in warm-blooded animals comprises administering to warm-blooded animals an immunomodulating effective amount of the product of the invention The product may be administered intraveneous route in bolus or continuous perfusion, by intramuscular, intraperitoneal, intrapleural or subcutaneous route. The usual daily dose depends on the conditions treated, the person concerned and method of administration. It can be 1.10⁶ U/M² /24 h to 40.10⁶ U/M² /24 h, and preferably 20.10⁶ U/M² /24 h in the adult or in the child.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is an analytic chromatogram of RP-HPLC of the crude extract in 8M guanidine of Example 1.

FIG. 1b is an analytic chromatogram of RP-HPLC of tile standard reduced and oxidized IL₂.

FIG. 2 is an analytic chromatogram of RP-HPLC of the "resolubilization" of Example 1.

FIG. 3 is a chromatogram of RP-HPLC of the "principal fraction" after the cooling stage of Example 1.

FIG. 4 is an analytic chromatogram of RP-HPLC of the fraction "59" of Example 1.

FIG. 5 is the purification protocol of Example 1.

FIG. 6 is the electrophoresis gel SDS-PAGE of Example 2.

FIGS. 7a and 7b are peptide charts of Example 2.

FIGS. 8a and 8b are the curves DC of Example 2.

FIG. 9 is the curve of mitogenetic effect on the human lymphocytes of Example 3.

FIG. 10 is the toxicity curve obtained with regard to the lines K 562 and DAUDI,

In the following examples there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

EXAMPLE 1

Purified reduced, biologically active r-hIL₂ starting from granules

Granules were obtained by centrifuging cultures of an E. coli strain transformed by a plasmide containing the coding sequence for natural IL₂ and capable of accumulating IL₂ in that form in the interio of the cells as described for example by Sato et al., J. Biochem (1987) Vol. 101 p 525-534!. The cells obtained from a 10 liter fermenter were subjected to an explosion in a Manton Gaulin homogenizer. Starting from isolated and washed cellular residue (90 to 170 g wet weight), the IL₂ was solubilized in 2.5 volumes of a Tris buffer, HCL 20 mM, pH 8, containing 8M guanidine hydrochloride (Gu,HCL) and 100 mM dithiothreitol (DTT). The solubilized amount of IL₂ (1.5 to 2.5 g) was estimated by analytic RP-HPLC on a C4 VYDAC column (0.46*15 cm) 300° A, 5 microns at a flow of 2 ml/mn, with a linear gradient of acetonitrile (30 to 70% in 10 minutes) containing 0.1% of TEA, a spectrophotometric detection at 280 nm or 210 nm, in which the surface of the peak was evaluated at 280 nm after calibration with a standard IL₂ (FIG. 1a and FIG. 1b). The IL₂ was then precipitated by lowering the concentration of Gu, HCL to 2M in the presence of DTT. After washing the precipitate with an aqueous solution of TFA at 0.1% until a pH value less than 5.0 was obtained for the supernatant, the IL₂ was solubilized in an aqueous solution with 20% of acetonitrile and 0.1% of TFA. The "resolubilization" obtained, which had a content of reduced IL₂ greater than 85% according to the analytic RP-HPLC (FIG. 2), had a biological activity lower than 0.01×10⁷ U/mg of reduced IL₂ and a content of sulfhydryl groups of 2.85 SH/mole of reduced IL₂. One fraction of the solution obtained, corresponding to approximately 200 mg of IL₂ estimated by the analytical RP-HPLC was diluted to adjust the concentration of acetonitrile to less than 10% in TFA at 0.1%, then applied to a C4 VYDAC column (5.7×30 cm). The IL₂ was eluted at a flow of 100 ml/mn with a linear gradient of acetonitrile (30 to 80% in 40 minutes) containing 0.1% of TFA, at a concentration of approximately 60% in acetonitrile in a major peak detected by spectrophotometry at 280 nm and analyzed by RP-HPLC, The "principal fraction" collected which contained the reduced IL₂ was then submitted to a slow cooling stage from ambient temperature to -20° C.±1° C. which allowed a superior organic phase which was rich in acetonitrile to be eliminated by decanting. The inferior phase, rich in water and containing the IL₂, was kept in a frozen state. After thawing, the solution obtained, after dilution by 2 volumes of a 0.5% aqueous solution of citric acid, was applied to a C4 VYDAC column (5.7×30 cm) which was developed with a linear gradient of isopropanol (20×70% in 40 minutes) containing 0.5% citric acid with a flow of 50 ml/mn. The effluent, followed by spectrophotometry at 280 nm, showed the successive elution of a minor peak at a concentration of approximately 48% in isopropanol (fraction "48") and a major peak at a concentration of approximately 59% isopropanol (fraction "59") (FIG. 3). The fraction "59" was collected and it was stable when kept at 0° C. for at least 24 hours and protected from air.

After elimination of isopropanol by azeotropic distillation in a vacuum, the "59" fraction was analyzed in analytical RP-HPLC and gave a homogeneous peak (FIG. 4) eluted with approximately 60% of acetonitrile whereas the reference oxidated IL₂ was eluted at approximately 57% of acetonitrile (FIG. 1b). The "59" fraction which, after elimination of the isopropanol, had a concentration of IL₂ greater than 1 mg/ml and a pH value of 3±0.5 was kept at +4° C. and protected from air for at least a week or it could be immediately lyophilized or formulated to obtain a pharmaceutical composition. The lyophilized "59" fraction was dosed in biological activity according to the in vitro test of the proliferation of the cells CTLL-2, and had a specific activity of 1.3±0.5×10⁷ U/mg similar to that of natural IL₂.

The content of free sulfhydryl groups of the lyophilized "59" fraction, determined by the colorimetric method with dithiodipyridine, was 2.94 SH/mole comparative to 0.76 SH/mole for the oxidized reference IL₂. 150 to 300 mg titrated by the analytical RP-HPLC of the reduced R-hIL₂ containing 3 SH groups, biologically active, homogenous in RP-HPLC, were obtained in the "59" fraction starting from a 10 liter fermenter (according to the protocol scheme FIG. 5).

EXAMPLE 2

Purification of the biologically active, reduced r-hIL₂

The procedure of Example 1 was repeated except that the "principal fraction" was not submitted to the cooling stage then to separation by decanting but was diluted immediately by 2 volumes of a 0.5% aqueous solution of citric acid. The "59" fraction was collected and treated as in Example 1.

EXAMPLE 3

Physiochemical characterization of the biologically active reduced r-hIL₂

The reduced r-hIL₂ obtained by the invention in the "59" fraction of Example 1 was examined for the following properties:

1) Homogeneity

The SDS PAGE electrophoresis was carried out on a gel in two phases (concentration gel and migration gel with 5% and 15% of acrylamide rsepectively) containing 10% of SDS. The sample was first heated for 2 minutes at 100° C. in a buffer with 3% of SDS and 5% of mercaptoethanol. The migration with a buffer at 1% of SDS was followed by coloration by silver which revealed a single band corresponding to a purity higher than 99% for a deposit of 2 ug (FIG. 6).

2) Molecular weight by electrophoresis

In a reducing medium, an apparent MW of approximately 15 Kd was determined in accordance with the calculaed MW of 15420 (FIG. 6).

3) Composition in amino acids

A sample containing 25 ug of the reduced r-hIL₂ of the invention in 0.5 ml of water was placed in a glass hydrolysis tube into which 0.5 ml of concentrated hydrochloric acid with 31.7% of TFA and 4.8% of thioglycolic acid were added. The tube was sealed under vacuum and then the hydrolysis was carried out at 155° C. for 40 minutes. The hydrolysate was then evaporated to dryness under reduced pressure. The residue was dissolved in 0.7 ml of a citrate buffer pH=3 and, then it was submitted to an amino acid analysis on an Interaction AA 511 column (0.46×15 cm) with a pH gradient (3 to 5) and sodium chloride (0 to 70 g/l) in the citrate buffer at 60° C. with a flow of 0.5 ml/mn and a detection by fluorescence, after derivation by orthophtal-aldehyde at the column outlet. The results are indicated in

Table 1 and the values are the average obtained for 2 repeated hydrolyses and 2 repeated chromatographs respectively. The composition was in agreement with that of natural IL₂ having a supplementary N-terminal methionine.

                  TABLE 1                                                          ______________________________________                                         INTERLEUKIN 2                                                                  Amino acids  Theoretical number                                                                          Number found                                         ______________________________________                                         GLN + GLU    18           17.56                                                ASN + ASP    12           12.61                                                THR          13           12.09                                                SER          8            7.05                                                 PRO          5            ND*                                                  GLY          2            2.59                                                 AKA          5            5.50                                                 VAL          4            4.34                                                 MET          5            5.59                                                 ILE          9            9.15                                                 LEU          22           19.96                                                TYR          3            2.60                                                 PHE          6            5.90                                                 TRP          1            NC**                                                 LYS          11           10.19                                                HIS          3            3.48                                                 ARG          4            5.29                                                 CYS          3            NC**                                                 ______________________________________                                          *ND = not detected                                                             **NC = not calculated                                                    

4) Sequence of N-terminal amino acid

The N-terminal sequence was identified by micro-sequencing using the Edman automatic degradation method. The analysis of 15 ug of biologically active, r-hIL₂ of the invention on a gas phase micro-sequencer Applied Biosystems 470 A coupled with HPLC 120 A allowed the following PTH amino acids to be identified:

    ______________________________________                                                Stages                                                                               PTH AA                                                            ______________________________________                                                1     Met                                                                            Ala                                                                      2     Ala                                                                            Pro                                                                      3     Pro                                                                            Thr                                                                      4     Thr                                                                            Ser                                                                      5     Ser                                                                      6     Ser                                                                      7     Ser                                                                      8     Thr                                                                      9     Lys                                                                      10    Lys                                                                      11    Thr                                                                      12    Gln                                                                      13    Leu                                                                      14    Gln                                                                      15    Leu                                                                      16    Glu                                                                      17    His                                                                      18    Leu                                                                      19    Leu                                                                      20    Leu                                                               ______________________________________                                    

The sequence of the 20 N-terminal residues is in agreement with the theoretical linking order of the natural IL₂ and approximately 10% of IL₂ without methionine was observed.

5) Peptide chart with cyanogen bromide

700 ug of reduced IL₂ residue of the invention (approximately 53 nmoles) were dissolved in 4 ml of 70% formic acid and 5.6 mg of cyanogen bromide were added. The solution was stirred overnight at ambient temperature, diluted with water, then lyophilized. The reaction mixture was analyzed by RP-HPLC on a uBondapack C18 RP column (0.46×20 cm), with a concentration gradient of acetonitrile varying from 0 to 70% containing 0.1% of TFA with a flow of 1 ml/mn at ambient temperature and with a spectrophotometric detection at 220 nm. The peptide chart of the reduced r-hIL₂ (FIG. 7a) showed a different fragmentation to that of the reference oxidized IL₂ (FIG. 7b).

6) Circular dichroism

The circular dichroism spectra (CD) were determined at ambient temperature on a Jobin Yvon Mark V spectrograph. The sample of reduced r-hIL₂ lyophilized after RP-HPLC carried out with a linear gradient of isopropanol in which the 0.5% citric acid according to Example 1 was replaced by formic acid at 0.1%, then distillation of the isopropanol and lyophilization, was taken up at a concentration of 1 mg/ml in acetic acid. The containers used were of 0.01 cm and 0.5 cm respectively for the peptide region (185-250 nm) and the aromatic region (260-320 nm) The solvent spectrum was subtracted from the spectrum of the IL₂ for each sample. The results are given in ellipticity 0 (average weight per residue of IL₂ =116).

FIG. 8a shows the CD spectrum in distant UV and the reduced biologically active r-hIL₂ of the invention, had a spectrum which indicated the presence of an ordered secondary structure. The determination of the alpha helix % showed little significant difference with the oxidized reference IL₂ (% alpha helix #50%). FIG. 8b showed the CD spectrum in near UV and the oxidized reference IL₂ had a significant DC which indicated an asymetric environment for the aromaic residues, whereas the reduced r-hIL₂ of the invention had a CD of little significance but different.

EXAMPLE 4

Biological activity

The biological effectiveness of the reduced r-hIL₂ of the invention was evaulated in the in vitro or ex vivo experiments.

1) In vitro activity on human cells

a. Lymphoblastic transformation test

Apart from the proliferative activity on cellular lines of mice such as CTLL-2 which allowed the biological measurement of IL₂, the reduced r-hIL₂ of the invention showed a mitogenetic effect) dependent on the dose, similar to that shown by the oxidized reference IL₂ on normal circulating human lymphocytes, shown by the measurement of the incorporation of the tritiated thymidine in ADN (FIG. 9).

b. The induction of the cytotoxicity of the mono-nuclear cells

The study is carried out with human circulating mononuclear cells incubated in the presence of IL₂ and of which the cytotoxic effect was determined with regard to tumoral target cells, the erythroleukemic line K 562 (sensitive to NK cells) and the DAUDI line derived from a B lymphome (resistant to NK cells) respectively, by measuring the salting out of CR 51 in 4 hours. The results, expressed in lytic units per 10⁶ cells (UL/10⁶), showed that the reduced r-hIL₂ of the invention shows a capacity depending on the dose, to increase the activity of NK or to induce the cytotoxicity of the T lymphocytes with regard to the tumoral targets respectively, in a manner similar to that known for natural IL₂ (FIG. 10).

2) Ex vivo activity on mice (stimulation of the peritoneal macrophages)

In normal Balb/c and MRL-+/+ mice, the successive intraperitoneal injections of recombinant interferon gamma of the rat in sub-optimal doses (100 to 3000 U), then 24 hours later, of reduced r-hIL₂ of the invention, released the oxidative mechanisms of the phagocyte cells, evaluated by measuring the chemiluminescence in the presence of phorbal ester (PMA) of the cells removed from the peritoneal cavity of the mice killed 24 hours after the IL₂ injection. The effect, depending on the dose, was similar to that seen with the oxidized reference IL₂ The results are reported in the following Table.

    ______________________________________                                                         Chemiluminescence (CPM × 10.sup.4)                       Injected dose   After injection of r-hIL.sub.2                                 (ng per mouse)  Reduced  Oxidated                                              ______________________________________                                         0                5 ± 2                                                                                4 ± 3                                             1                7 ± 3                                                                                5 ± 1                                             3               90 ± 5                                                                               71 ± 5                                             10              130 ± 10                                                                             140 ± 70                                           30              350 ± 50                                                                             400 ± 70                                           100             710 ± 20                                                                             695 ± 25                                           300             375 ± 25                                                                             350 ± 20                                           ______________________________________                                    

EXAMPLE 5

Pharmaceutical composition for injection

The aqueous solution of reduced r-hIL₂ corresponding to the "59" fraction of the invention, from which the isopropanol had been eliminated by azeotropic distillation in a vacuum, was extemporaneously diluted with an aqueous solution of mannitol degassed and saturated with nitrogen at the rate of 100 ug of reduced IL₂ ml and 50 mg/ml of mannitol. After filtration on a 0.22 u membrane, sterile distribution of 1 ml in flasks and lyophilization, the flask-doses were stoppered in a nitrogen atmosphere and kept at a temperature of +4° C. before use.

EXAMPLE 6

Pharmaceutical composition by continuous perfusion

The aqueous solution of reduced r-hIL₂ corresponding to the "59" fraction of the invention from which the isopropanol had been eliminated by azeotropic distillation in a vacuum was extemporaneously diluted with an aqueous solution of mannitol, degassed and saturated with nitrogen at the rate of 500 ug of reduced IL₂ /ml and 50 mg/ml of mannitol. After filtration on a 0.22 u membrane, sterile distribution into 1 ml flasks and lyophilization, the flask doses were stoppered under a nitrogen atmosphere and kept at a temperature of 4° C. until use. The contents of each flask was then dissolved by injection of 1 ml of sterile distilled water and the solutions corresponding to 7 flask doses (approximately 35.10⁶ units) were introduced in a Viaflex^(R) container containing 500 ml of solution for Travenol^(R) glucose at 5% perfusion.

Various modifications of the compositions and method of the invention may be made without departing from the spirit or scope thereof and it should be understood that the invention is intended to be limited only as defined in the appended claims. 

What we claim is:
 1. Non-glycosylated, recombinant human IL-2 in reduced form, having a specific activity of at least 0.5×10⁷ U/mg, and prepared by a process comprising the sequential steps of:extracting IL-2 from inclusion bodies in a transformed microorganism by solubilization in a reducing medium with a chaotropic agent; precipitating the IL-2; resolubilizing and purifying the precipitated IL-2 on a reverse phase high performance liquid chromatography (HPLC) column with an acid eluant; cooling the principal fraction from the HPLC to about -20° C. to form an aqueous phase and an organic phase; recovering the aqueous phase and diluting the same in an acid medium; purifying the IL-2 on a second reverse phase HPLC column in an acid medium; and recovering the IL-2.
 2. A composition comprising the purified IL-2 of claim 1, citric acid, mannitol, and an aqueous solvent.
 3. A pharmaceutical composition comprising the IL-2 of claim 1 in an amount effective to modulate an immune function in a subject, an organic acid, and an inert pharmaceutical carrier.
 4. A pharmaceutical composition according to claim 3, wherein the organic acid is citric acid and the composition additionally comprises mannitol. 